Interactive display devices have been produced by integrally combining operation surfaces using touch panels and video-display surfaces (hereinafter, referred to as display screens). Users may operate buttons and figures displayed on display screens. At this time, display devices suffer from problems due to blots or blemishes formed on display screens, which may reduce the accuracy of recognizing user's operations or visibility for users.
Patent Literature 1 discloses a display device for improving a reduction of visibility due to blots. The display device disclosed in Patent Literature 1 counts the number of times each user touches the display screen for each pixel. In addition, it determines a degree of fouling for each pixel based on the number of times each user touches the display screen. Therefore, it determines a display manner based on the degree of fouling determined above.